Cracks in terrazzo: along the divider strips or across the room

Most cracks in a Tampa terrazzo floor follow the slab underneath, often along the divider strips, and most are repairable at a typical $75 to $250 per patch. Hairline cracks get a tinted fill; wider ones get a fill with matched chips; badly broken sections are replaced from strip to strip. Done before the $5 to $9 per square foot grind, the repairs come up with the floor and blend.

Check this first

1. Measure the width. A crack you cannot fit a fingernail into is hairline. The NTMA restoration specification classes hairline cracks as under 1/32 inch. A crack you can lay a coin edge in is a real crack.
2. Check for a step. Run a fingertip across it. If one side is higher, the slab has moved vertically, which needs a closer look before patching.
3. Note where it runs. Along a divider strip, across a whole room in a straight line, or in a spider web from one spot. Each points to a different cause.
4. Mark the ends. Put a pencil tick at each end and the date. If the crack grows past the ticks over a few months, it is still moving.
5. Tap beside it. A hollow sound next to a crack means the topping has let go there. See hollow-sounding terrazzo.

What is behind it

Why cracks follow the slab

A thin house terrazzo floor is typically what the NTMA calls a monolithic system: a nominal half-inch cement topping bonded straight to the slab and, in the NTMA’s words, dependent on the quality of the concrete slab for flatness and crack prevention. When the slab cracks, the topping cracks with it. Where a divider strip sits over a joint in the slab, that is often where the movement shows, which is why so many cracks run beside a strip. The NTMA is also clear that strips not over a concrete joint are strictly decorative and do not prevent cracks, so a crack running across a panel is no sign the strips failed. On a slab that has been shrinking and settling since the 1950s or 1960s, a fine crack is a normal sign of age.

That age is real across our area. In our pull of 1,103 Hillsborough County property records, every house that listed terrazzo was built between 1954 and 1970. On West Country Club Drive in Forest Hills, the terrazzo listings date from 1954 to 1960. Floors that old have had decades to follow every movement of the slab.

How the NTMA approaches it

The NTMA’s restoration guide specification sets out a clean process. Owner and contractor walk the floor and mark each crack as one of three: no action, repair crack or replace terrazzo. Repairs clean out the crack, fill it with resin to match, and add aggregate in any crack wider than a quarter inch. Replacement runs to an architectural break, usually the nearest divider strip, or to a jagged, saw-tooth edge where there is none, because a straight cut across a panel draws the eye. We work the same way, and we walk your floor with you before anything is cut.

What it will look like

A filled hairline crack beside a strip nearly disappears once the floor is ground and polished. A wider crack filled with chips reads as a slightly different line of terrazzo up close. A replaced panel reads as one panel in a slightly different shade, because, as the NTMA says, matching existing aggregates may not be exact. The crack and hole repair page explains how chips and matrix are matched.

When to call

When the covering is off and you can see all the cracks. Send a photo of each with a coin beside it, and tell us whether any have a step or are growing. You get a crack-by-crack plan and a range from the pricing page. For a floor that only needs patching, the repair visit estimator adds it up.